This application claims priority to Korean Patent Application No. 10-2004-0061420, filed on Aug. 4, 2004, in the Korean Intellectual Property Office, the disclosure of which is incorporated herein in its entirety by reference.
1. Field of the Invention
The present invention relates to a wired/wireless communication system and, more particularly, to a wired/wireless communication receiver including an improved equalizer and a communication method.
2. Description of Related Art
Devices such as computers and mobile communication terminals connected to a LAN (local area network) for wired/wireless communications transmit/receive data using communication signals. A CCK (complementary code keying) signal defined by IEEE 802.11, one of the communication signals, is transmitted/received at a transfer rate of maximum 11 Mbps in a frequency band of 2.4 GHz.
Signals transmitted from a transmitter fade while passing through a multipath channel environment and the fading signals are received by a receiver. The multipath fading causes a signal delay and inter-signal interference. This inter-signal interference generates transmission error and brings about degradation of the performance of the receiver. The receiver needs equalization for compensating signal distortion, interference and energy loss generated when signals are transmitted through a multipath. A transmission theory about radio LAN signals such as the CCK signal is disclosed in detail in U.S. Pat. No. 6,256,508 and U.S. 2002/0159422.
FIG. 1 illustrates a chip, a symbol and a frame of a received signal. Referring to FIG. 1, when a CCK signal is QPSK-modulated (quadrature phase-shift keying-modulated), one symbol can include eight chip codes and each chip code can include signal components having four phases. A plurality of symbols comprise one frame. The signal composition can have different protocols when it is modulated by other modulation methods including BPSK (binary phase-keying) modulation.
FIG. 2 illustrates an example of RMS (root mean square) power delay profile of a signal received through a multipath channel. The signal passing through the multipath channel arrives at a receiver with delay time varying with path lengths Ts through 8Ts. The power of the received signal can be exponentially reduced in response to the delay time. The power of the received signal can be calculated from the magnitude of a CIR (channel impulse response). For example, the four signal components comprising each chip of FIG. 1 appear as a CIR in the receiver.
An equalizer of the receiver uses an FIR (finite impulse response) filter and compensates signal distortion, interference and energy loss caused by multipath delay. The FIR filter generates delay signals, respectively multiplies the delay signals by predetermined coefficients, and sums up the multiplied signals. The delay signals are obtained by delaying an input signal by sampling time. The number of multipliers multiplying the delay signals by the predetermined coefficients or the number of the predetermined coefficients corresponds to the number of taps of the FIR filter. In a long multipath channel environment having a large delay, compensation performance is generally improved as the number of taps is increased. However, in a short multipath channel environment, the compensation performance is not always improved in proportion to the number of taps in the equalizer. In the case where the number of taps of the FIR filter is increased excessively in the short multipath channel environment, signal interference is further increased when delay signals having a large delay are synthesized to degrade the performance of compensating received signals.